Method for determining a current glucose value in a transported fluid

Abstract

The invention relates to a method in particular for continuously determining a current glucose value in a transported fluid, in particular blood, of an organism, having the steps of: a) ascertaining a series of measurements, comprising at least two measurement values separated by time intervals, for a tissue glucose value in the tissue surrounding the transported fluid using a sensor device, b) ascertaining the tissue glucose value using the ascertained series of measurements on the basis of a sensor model, wherein measurement values of the sensor device are assigned to tissue glucose values while taking into consideration measurement noise using a sensor model, c) providing a state transition model, the ascertained tissue glucose values being assigned at least one glucose value in the transported fluid using the state transition model while taking into consideration process noise, and d) ascertaining the current glucose value on the basis of the provided state transition model and the ascertained tissue glucose value. At least step d), in particular steps b)-d), is carried out using at least one moving horizon estimation method.

1 . A process to, preferably continuously, determine a current glucose level in a transport fluid, particularly blood, of an organism, comprising the steps
 a) determining, using a sensor device, a series of measurements, comprising at least two measurements separated in time for a tissue glucose level, in the tissue surround the transport fluid,   b) determining the tissue glucose level using the series of measurements given, based on a sensor model, in which, by means of a sensor model, measurements of the sensor device are correlated to the tissue glucose levels while taking into account measurement noise,   c) providing a state transition model, in which, by means of the state transition model, at least one glucose level in the transport fluid is correlated to the tissue glucose levels that have been determined while taking into account process noise, and   d) determining the current glucose level based on the state transition model that has been provided and the tissue glucose level that has been determined,   in which, at least step d), particularly steps b)-d), is carried out using at least one Moving Horizon Estimation Method, preferably a Moving Horizon Estimation method is carried out to provide the current glucose level in step d) and applied to previously provided glucose measurements and at least one previous tissue glucose measurement.   
     
     
         2 . The process according to  claim 1 , characterized in the sensor model is provided in the form of a linear or non-linear function between measurements and tissue glucose levels. 
     
     
         3 . The process according to  claim 1 , characterized in that the value for the horizon of the Moving Horizon Estimation method for providing the current glucose level is selected as less than or equal to 10. 
     
     
         4 . The process according to  claim 1 , characterized in that a variance of the measurement noise and/or the variance of the process noise, particularly at least on a regular basis, is estimated or especially interpolated and/or weighted, preferably where the variance of the measurement noise and/or the variance of the process noise is estimated on the basis of at least one previous value, especially interpolated and/or weighted, using an exponential smoothing. 
     
     
         5 . The process according to  claim 4 , characterized in that measurements that have only partially used to calculate the estimation of the measurement noise and/or of the process noise can be temporarily stored, and measurements that have not been temporarily stored and that are needed can be interpolated using the measurements that have been stored. 
     
     
         6 . The process according to  claim 3 , characterized in that a selection is made of a quantity of the previous measurements, which is greater than the measurement for the horizon of the Moving Horizon Estimation method, in particular at least twice as great, preferably at least by the factor 5. 
     
     
         7 . The process according to  claim 4 , characterized in that the variance of the measurement noise and/or the variance of the process noise is regularly adjusted based on the level of the sum of the horizon of the Moving Horizon Evaluation method and the number of the previous measurements to calculate the estimation of the measurement noise and/or the process noise. 
     
     
         8 . The process according to  claim 1 , characterized in that measurements provided by means of a filter function are filtered by means of a filter function, whereby, by means of the filter function, errors, especially measurement errors, are suppressed by the sensor device, preferably whereby measurements are weighted by means of the filter function. 
     
     
         9 . The process according to  claim 8 , characterized in that, in order to determine errors of the sensor device, the gradient of the increase in a current tissue glucose level and/or the current tissue glucose level is evaluated. 
     
     
         10 . The process according to  claim 8 , characterized in that measurements that are provided below a low threshold level that can be preset and/or above a high threshold level that can be preset are discarded by means of the filter function, particularly the low and high threshold level corresponds to physiological limits, preferably where the low threshold level presents a value between 10-50 mg/dL, particularly 30 mg/dL and the high threshold level presents a value between 100-600 mg/dL, preferably 450 mg/dL. 
     
     
         11 . The process according to  claim 1 , characterized in that a calibration of the measurements of the sensor device is executed after execution of step d). 
     
     
         12 . The process according to  claim 1 , characterized in that the state transition model includes a diffusion model for time-dependent modeling of the diffusion process of glucose from the transport fluid into the surrounding tissue, and/or
 sensor model parameters of the sensor model and/or state transition parameters of the state transition model are estimated and/or updated, at least on a regular basis.   
     
     
         13 . A device to, preferably continuously, determine a current glucose level in a transport fluid, particularly blood, of an organism, preferably suitable for carrying out a process according to  claim 1 , comprising
 a sensor device, particularly for measuring fluorescence in a tissue surrounding the transport fluid, by means of a fiber optic probe, designed to determine a series of measurements, comprising at least two measurements separated in time for a tissue surrounding the transport fluid,   a provision device designed to provide a state transition model, in which, by means of the state transition model, at least one glucose level in the transport fluid is correlated to the determined tissue glucose levels while taking into account process noise, and to provide a sensor model, in which, by means of a sensor model, measurements of the sensor device are correlated to tissue glucose levels taking into account measurement noise,   an evaluating device designed to determine the tissue glucose level, using the series of measurements provided, based on the sensor model and to determine the current glucose level based on the state transition model that has been provided and the tissue glucose level that has been ascertained, using a Moving Horizon Estimation Method.   
     
     
         14 . An evaluation device to, preferably continuously, determine a current glucose level in a transport fluid, particularly blood, of an organism, preferably suitable for carrying out a process according to  claim 1 , comprising at least one interface to connect a sensor device to provide a series of measurements, comprising at least two measurements separated in time for a tissue glucose level, in which the tissue surrounding the transport fluid,
 at least one memory to store a state transition model, in which, at least one glucose level in the transport fluid is correlated to the tissue glucose levels by means of the state transition model while taking into account at least one process noise level, and to store a sensor model, in which, by means of the sensor model, measurements of the sensor device are correlated to tissue glucose levels while taking into account at least one measurement noise, and   a calculating device designed to determine the tissue glucose level, using the series of measurements provided, based on the sensor model and to determine the current glucose level based on the state transition model that has been stored and the tissue glucose level that has been determined, using at least one Moving Horizon Estimation Method.   
     
     
         15 . A non-tangible, machine-readable medium for the storage of instructions, which, when carried out on a computer, cause a process, particularly, to continuously determine a current glucose level in a transport fluid, particularly blood, of an organism, to be carried out preferably suitable for carrying out a process according to  claim 1 , comprising the steps
 a) determining, using a sensor device, a series of measurements, comprising at least two measurements separated in time for a tissue glucose level, in the tissue surround the transport fluid,   b) determining the tissue glucose level using the series of measurements given, based on a sensor model, in which, by means of a sensor model, measurements of the sensor device are correlated to the tissue glucose levels while taking into account measurement noise,   c) providing a state transition model, in which, by means of the state transition model, at least one glucose level in the transport fluid is correlated to the tissue glucose levels that have been determined while taking into account process noise, and   d) determining the current glucose level based on the state transition model that has been provided and the tissue glucose level that has been determined,   in which, at least step d), particularly steps b)-d), is carried out using at least one Moving Horizon Estimation Method.